Study suggests limits to global warming

DURHAM, N.C. (UPI) -- Duke University scientists say ancient and modern evidence suggests there are limits to future global warming.

A Duke-led team ran some 1,000 computer simulations, covering 1,000 years, to obtain a long-range climate change assessment. By analyzing indirect evidence of temperature fluctuations during a 6-century period, the researchers determined the magnitude of future global warming will likely fall well short of the current highest predictions.

The computer simulations took into account modern records that are based on thermometer readings, as well as such measurements as tree rings and ice cores that served as markers of warm and cold conditions during prior centuries.

The commonly accepted range for how much average global temperatures will rise in response to a doubling of atmospheric carbon dioxide is between 1.5 and 4.5 degrees centigrade, with some observational studies suggesting the possibility of a rise exceeding 9 degrees centigrade.

However, the study -- using "reconstructions" of Northern Hemisphere temperatures since the year 1270 -- showed a reduced likelihood the actual maximum increase will exceed 4.5 degrees -- "from 36 percent to 15 percent or less," the researchers said.

The study is detailed in the journal Nature.